For example, in a winding device (including a rewinding function) for a belt-like or string-like long-length material, a retracting drum (also referred to as a drum or a spool) that winds the long-length material is rotationally moved relative to a supporting unit that rotatably supports the retracting drum. In such a device that performs relative rotational movement, since a large load is applied to the device or the long-length material when the long-length material is fully extended or when the retracting drum is stopped while winding or rewinding, it is preferable that an energy absorbing device is disposed between objects that perform relative rotational movement. As an example of such a winding device, a seat belt retractor that is used for a seat belt device is representative (e.g., see Patent Literature 1 or 2).
Patent Literature 1 discloses a seat belt retractor, in which a torsion bar and a wire are disposed between a winding drum and a ratchet gear that are rotationally moved relative to each other. According to such a seat belt retractor, torsional deformation of the torsion bar and sliding deformation of the wire can absorb energy that may be generated between the winding drum and the ratchet gear, and by making a difference in a pull-out load required for the sliding deformation of the wire, an energy absorption characteristic can be changed.
Patent Literature 2 discloses a force limiter device for a vehicle, in which ring disks (1 and 3) and a swing member (2) are disposed between objects that perform relative rotational movement. According to such a device, when the swing member (2) is rotated relatively to the ring disks (1 and 3), a projection (5) formed to the swing member (2) comes into contact with projections (7 and 8) formed to the ring disks (1 and 3) while alternately swinging, which enables absorption of energy generated between the objects that perform relative rotational movement. In this device, particularly, while kinetic energy changes according to a rotational speed of the swing member (2), an increase in the rotational speed of the swing member (2) can increase the energy absorption amount.